Direct Access to Poly(amino ester)s with Main-Chain H-Bonding Motifs.

Abstract

We report a novel alternating copolymerization of epoxides and N-carboxyanhydrides as a direct synthetic route to polyesters bearing hydrogen-bonding motifs in their main chain, thereby enabling the straightforward synthesis of a previously inaccessible class of poly(amino ester)s featuring secondary amines. Conventional strategies for preparing functionalized polyesters are confined to side-chain modifications, often requiring postpolymerization functionalization to introduce versatile functionalities. However, our synthetic approach directly incorporates secondary amine moieties into the polymer backbone and allows the characterization of the corresponding hydrogen bonds. Through a combination of experimental spectroscopic analysis and density functional theory calculations, we demonstrate that hydrogen bonding from the amine moieties plays a critical role in activating the epoxide monomers, a mechanistic insight that distinguishes this system from conventional copolymerizations. Furthermore, we characterize the robust hydrogen-bonding network within these polymers that contributes to their high thermal stability, with Td,5% (temperature at 5% weight loss) values reaching up to 315 °C. Finally, the polymers undergo selective base-catalyzed hydrolysis of the ester linkages, demonstrating their degradability, and the polymerization is compatible with a bifunctional epoxide bearing a poly(ethylene glycol) chain to afford a water-soluble amphiphilic graft copolymer.